Twenty Twenty-Five: Update text strings

[carolinan]

In Twenty Twenty-Five:

Remove the unnecessary context from some text strings where the translatable text was the same but the context was different. This reduces the number of strings a translator needs to work with.

Update the name of headers, to make it easier for translators to understand that they are site headers not headings.
Update the name of templates to make the naming more consistent.
Example:
Title: Text-only blog, home is now Title: Text blog home to match Title: News blog home etc.

Trac ticket: https://core.trac.wordpress.org/ticket/62482

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